The present invention relates generally to aircraft manufacturing, and, more specifically, to adhesive metal bonding of components therein.
Aircraft typically included many parts and sections made from high strength aluminum for reducing weight. The aluminum parts are typically bonded together mechanically by fasteners and rivets, or by using high strength adhesive where appropriate.
Vacuum bagging is one method for adhesively bonding together metal components in contrast with its common use in fabricating composite laminates of fibers in a cured resin matrix.
In metal bonding, an adhesive film is applied between the metal parts and enclosed in a vacuum bag to clamp the parts together, and then the adhesive is thermally cured in a predetermined curing cycle typically conducted at elevated temperature and pressure for a specified time duration.
The initially solid adhesive film softens during thermal curing and decreases in viscosity as temperature rises. The softened adhesive may then leak from the bond area to form a small fillet or flash of cured adhesive extending outwardly from the bonded joint.
This cured flash may be undesirable in the aircraft part for its additional weight, or interference with adjoining parts, or simply for cosmetic appearance.
Removal of unwanted adhesive flash may therefore be accomplished by various post-bonding processes, which correspondingly require suitable equipment and labor which increase production time and cost. Such flash removal processes include sanding, grinding, scraping, and grit blasting with wheat-starch for example, and may adversely affect the corrosion protection of the underlying aluminum parts, which in turn requires rework to restore that corrosion protection.
In order to minimize flash during the vacuum bagging bonding of metal components, a specialized flashbreaker tape is available for locally masking the edge of the bond joint so that the adhesive leaks atop the tape, and may be simply removed after curing by removing or tearing away the tape and so captured flash.
Alternatively, a specialized pressure strip is also available to block adhesive seepage from the bond joint during curing.
However, since both products are specialized, their use increases complexity of the vacuum bagging process and correspondingly increases manufacturing cost, and may also have adverse effects.
For example, the flash is torn with the removal of the flashbreaker tape, and can leave an undesirable rough adhesive edge at the joint. And, the pressure strip merely dams the viscous adhesive as the metal parts are compressed during curing, with the full volume of the flash, and its weight, remaining in the bonded assembly.
Accordingly, it is desired to provide an improved vacuum bagging metal bonding process which reduces formation of undesirable flash during thermal curing.